1. Field of the Invention
The present invention relates to an improved circuit interrupting device and more particularly, to single or multi-gap interrupting devices, which utilize a puffing principle.
2. Discussion of the Prior Art
Circuit interrupting devices of a wide variety of types are well-known. Such devices include, fuses, circuit breakers, reclosers, circuit-switchers, and similar and related devices having various common and commercial names. Specifically, most if not all of these devices perform circuit interruption of two primary actions. The first action involves the intentional formation of an arc upon separation of a pair of normally engaged contacts, between the separating contacts. The arc is elongated as the contacts separate and this elongation aids in extinguishing the arc and interrupting the circuit. The second primary action involves the use of a specialized medium, or environment, in which the arc is formed. This environment may include one of a large number of materials which are inimical to arcs. Many fuses utilize so-called ablative arc-extinguishing materials such as boric acid. When the arc impinges on the boric acid, large quantities of turbulent, cooling and deionizing gases are rapidly evolved. The action of these gases in conjunction with arc elongation ultimately extinguishes the arc. At times, in non-fuse circuit interrupting devices, similar ablative materials are used. However, in many non-fuse circuit interrupting devices, liquid or gaseous media are provided which aid in circuit interruption. Typical of such a medium, is sulphurhexafluoride (SF.sub.6)Sulphurhexafluoride has excellent dielectric and arc-extinguishing properties. However, it has been found, especially at particular voltages and currents, that the mere presence of sulphurhexafluoride in insufficient to ensure arc extinguishment in conjunction with arc elongation. As a consequence, a wide variety of devices have been evolved in which the sulphurhexafluoride is puffed, or otherwise caused to flow at a high rate in the vicinity of the arc as it is being extinguished. These types of circuit interrupting devices are often referred to as "puffer" circuit interrupting devices.
Circuit interrupting devices of the puffer type have tended in the past to be very complicated and extremely difficult to assemble in addition to being quite expensive. Accordingly, one object of the present invention, is the provision of a circuit interrupting device, which is simple in construction and operation, inexpensive to manufacture, and consequently, inexpensive to the buyer.
The various types of known circuit interrupting devices have varying operational characteristics and features, which make their use technically attractive in some environments, but technically less attractive in others. In the past, operational features tended to be the only criteria determining which type of device was to be used. Today, however, the relative cost of the device is becoming an important, if not the most important, determinant in deciding which device shall be used in a particular environment. Users of these devices are today often willing to forego purchasing exotic, broad-range, interrupting capability devices in favor of inexpensive, simple devices, even though the latter may have more limited interrupting capabilities.
One use environment in which users today are inclined to employ less expensive, simple devices, is that of transformer protection. Devices which up to now have been employed for transformer protection have been either (1) complicated or expensive, or both, or (2) simple and inexpensive, but not reusable. Economic conditions have forced equipment users, especially utilizes, to consider employing transformer protective devices which are not broad-range, and are therefore less versatile or sophisticated, but which are at the same time substantially less expensive. Specifically, many utilizes have come to realize that there are times when it is expeditious to use an inexpensive interrupting device having a more limited interrupting rating, as opposed to a broad-range interrupting device, if the inexpensive device is sufficiently less expensive that alternative broad-range devices, so as to make the use of the former attractive from a capital investment standpoint. The attractiveness of such inexpensive devices is enhanced if they are reusable. Thus, a further object of the present invention is the provision of a reliable, inexpensive, simple and reusable interrupting device having limited interrupting capabilities.
If a broad-range device such as a circuit breaker is used as a sole device protecting a transformer, several potential negative aspects, in addition to its high cost, may be present. First, impedance of the transformer, and of the conductors between the transformer and the breaker, may so limit currents on the transformer's primary caused by secondary faults, that the breaker does not timely respond. Second, because of the high cost, it is often expedient to apply breakers to protect several branch circuits fed by a larger transmission or distribution circuit. In this event, operation of the breaker, due to a secondary fault in a transformer located in one such branch circuit, de-energizes all such branch circuits. Thus, a fault in one part of a system may render inoperative a large portion of the system. If the breaker is moved closer to the transformer, and does not involve branches other than the one in which the transformer is located, if may be under-utilized, having the ability of more extensive system protection. Such under-utilization is unattractive from a cost standpoint. Accordingly, another object of the present invention is the provision of the circuit interrupting device, which from a cost standpoint, is not under-utilized in providing limited protection for a limited portion of an electrical circuit.
Placement of a relatively cheap protective device--such as a fuse--intermediate a breaker (protecting several branches) and the transformer (in one of the branches) is an obvious expedient. However, until recently, choices of such cheaper devices have been limited. Moreover, where fuses are used, they must be replaced or replenished following performance of their protective function. Fuse-like devices which are reliable, relatively inexpensive, and partly reusable have only lately become available. See, for example, the following commonly-assigned U.S. patents and patent applications: Ser. No. 909,144 filed May 24, 1978 and U.S. Pat. Nos. 4,183,005 issued Jan. 8, 1980 in the names of O. Meister and T. J. Tobin; and 4,161,711 issued July 17, 1979 in the name of O. Meister. Nevertheless, another object of the present invention is to provide a reliable, inexpensive, and reusable, limited fault capability device, as an alternative to fuses, fuse-like devices, and breakers, for placement between a transformer and a more expensive broad-range interrupting device.
Yet another object of the present invention, is the provision of a simple, reliable, inexpensive interrupting device, having a limited interrupting rating, but which nevertheless is attractive in view of its low cost, which is completely bus- or line-mountable, and which operates entirely on bus or line potential. Such a device is even more attractive should its entire sensing and "intelligence" be at line or bus potential, thus obviating the need for complex interconnections between the interrupting device and its "intelligence" and sensing. From a cost standpoint, it is also desirable that such a device be usable and manually resettable from the ground to obviate the necessity of expensive and complicated reclosing mechanisms. Toward these ends, the circuit interrupting device of the present invention, is usable with an operating mechanism disclosed in a co-pending, commonly assigned, U.S. patent application Ser. No. 930,774, filed Aug. 3, 1978 in the names of J. Opfer and K. Vojta. The operating mechanism of the last-mentioned patent application is entirely at line or bus potential as is its "intelligence." The operating mechanism and its "intelligence" are intended to sense current conditions in the circuit in which the circuit interrupting device is connected to selectively operate the device in accordance with those current conditions. If it is desired to also add a so-called "shunt trip" mechanism to the device, such may be of the type disclosed in co-pending, commonly assigned, co-filed U.S. patent application, Ser. No. 951,681, filed Oct. 16, 1978 in the names of J. Bernatt and K. Vojta. The "shunt trip" mechanism in the last-mentioned patent application, effects operation of the circuit interrupting device depending upon the occurrence of events other than the condition of the current in the circuit being protected. Such other events include over-pressure in a transformer being protected, undesirable differential currents in the transformer, or simply, the opening or interrupting of the circuit in order to perform normal maintenance or repair.
Circuit interrupting devices which rely on fluids or gases such as SF.sub.6 for extinguishing arcs, generally involve sealed housings surrounding the elements of the device which interrupts the circuit. It is generally desirable to maintain the SF.sub.6 within the housing at a predetermined, super-atmospheric pressure, slightly in excess of one atmosphere. If the pressure of the gas within the housing reaches too high a level for whatever reason, there is a danger that the housing may fracture or break. Additionally, if the pressure of the gas or the housing falls to too low a level, there is the possibility that the arc-extinguishing capability of the device may be hindered if not eliminated. Accordingly, the circuit interrupting device of the present invention, may also be used with a combined pressure relief and pressure indicating mechanism disclosed in commonly assigned, co-pending, co-filed U.S. patent application Ser. No. 951,686, filed Oct. 16, 1978 in the name of J. Bernatt. The mechanism of this last named Patent Application, both indicates the presence of a too low pressure in the housing and automatically relieves over-pressures therewithin.
Another overall object of the present invention is therefore aimed at the provision of a simple, reliable, low-cost circuit interrupting device for use in a variety of environments and with a variety of operating mechanisms, shunt trip mechanisms and other associated mechanisms, wherein fault interrupting ability is achieved at low cost.